1. Field of the Invention
The present invention relates to a sintered polycrystalline diamond composite for use in rock drilling, machining of wear resistant materials, and other operations which require the high abrasion resistance or wear resistance of a diamond surface. Specifically, this invention relates to such bodies that include a polycrystalline diamond layer attached to a cemented carbide substrate via processing at ultrahigh pressures and temperatures.
2. Description of the Art
It is well known in the art to form a polycrystalline diamond cutting element by sintering diamond particles into a compact using a high pressure, high temperature (HP/HT) press and a suitable catalyst sintering aid. Apparatus and techniques to accomplish the necessary sintering of the diamond particles are disclosed in U.S. Pat. No. 2,941,248 to Hall and U.S. Pat. No. 3,141,746 to DeLai.
U.S. Pat. No. 3,745,623 Wentorf et al. teaches sintering of the diamond mass in conjunction with tungsten carbide to produce a composite compact (PDC) in which the diamond particles are bonded directly to each other and to a cemented carbide substrate.
Diamond compacts and PDC manufactured in accordance with the teachings of DeLai and Wentorf et al. have been limited to low-temperature applications since they show significant thermal damage at temperatures above approximately 750° C. The thermal degradation results in accelerated wear when such compacts are employed in high-temperature applications such as in rock drilling.
A solution to this problem has been proposed in U.S. Pat. No. 5,127,923 to Bunting whereby a diamond cutting element is produced by subjecting a mass of abrasive particles, e.g. diamond or cubic born nitride, to multiple pressure cycles at high temperatures. A solvent-catalyst sintering aid is employed in the initial pressure cycle to form a compact. Depending upon the degree of sintering, the solvent-catalyst can be removed by leaching or other suitable process. During a second pressure cycle, the compact can be bonded to a supporting substrate. In addition, a non-catalyst sintering aid, such as silicon, boron or metals rendered non-catalytic by the addition of silicon or boron which may form strong and chemically-resistant carbides, can be used in the second pressure cycle to enhance the sintering process and create a hard abrasive bonding matrix through out the particle mass.
A problem with this approach is that the polycrystalline diamond layer that is formed during the first high-pressure/high-temperature cycle must be precision ground prior to placing it on top of a substrate for the final high-pressure/high-temperature bonding step. This significantly increases the cost and results in a significantly lower yield than producing PDC in a single step operation. Another disadvantage is the bond between the polycrystalline diamond layer and the substrate is not nearly as strong as that for PDC which is made in a single high pressure cycle whereby individual diamond crystals are bonded to a substrate and to each other. The diamond layer on PDC made by this prior art method often spontaneously delaminates from the substrate before or during use on drill bits or other tools.
Another solution to this problem has been proposed in U.S. Pat. Nos. 6,878,447, 6,861,137, 6,861,098, 6,797,326, 6,739,214, 6,592,985, 6,589,640, 6,562,462 and 6,544,308 to Griffin. This solution provides a cutting element wherein a portion of the diamond table is substantially free of the catalyzing material, and the remaining diamond matrix contains the catalyzing material.
According to these patents, a portion of the diamond table of the PCD element is post-processed so that the interstices among the diamond crystals are substantially free of the catalyzing material. The portion of the diamond table that is substantially free of the catalyzing material is not subject to the thermal degradation encountered in other areas of the diamond body, resulting in improved resistance to thermal degradation. In cutting elements, the processed portion of the diamond body may be a portion of the facing table of the body, a portion of the peripheral surface of the body, or portions of all these surfaces.
A problem with this approach is that it is difficult to leach the catalyst sintering aid if the polycrystalline diamond working surface is highly consolidated with strong diamond to diamond bonding. Typically PDC for rock drilling is made from a blend of diamond with different particle sizes giving an average particle size of less than 25 microns. This results in a dense diamond table and it is very difficult to remove the catalyst. Even with diamond particle sizes as large as 40 microns it can become problematic to remove the catalyst if sintering conditions are such that extensive diamond to diamond bonding reduces the size of the interconnected pore network. To alleviate this problem, addition of non-catalytic fillers or lower pressure sintering conditions are necessary in order to create a large enough area of interconnected pores so that acids or other materials can effectively penetrate the diamond network to remove the catalyst. This reduces the impact and abrasion resistance of the finished PDC.
It is desirable to produce a more thermally stable PDC without having to go through the time consuming and costly steps of having to leach out the solvent catalyst from a densely formed and well bonded diamond layer.